Electrically-conductive grid shield for semiconductors

ABSTRACT

An electrically-conductive grid placed between an LED and a photodiode prevents false triggers of the photodiode by transient electrical fields. The grid terminates the field but allows light output of the LED to pass to the photodiode.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a divisional application of and claimspriority from Ser. No. 09/547,475 filed Apr. 12, 2000 and entitled“ELECTRICALLY-CONDUCTIVE GRID SHIELD FOR SEMICONDUCTORS” herebyincorporated herein by reference in its entirety.

BACKGROUND

[0002] In semiconductor devices, a transient electrical field may inducecurrents that result in false indications. Optocouplers may beespecially susceptible to such phenomena when a high voltage pulse isreceived at the input stage. To overcome this problem, anelectrically-conductive shield is provided to terminate and dissipatethe electrical field while allowing light to pass.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003]FIGS. 1 and 2 are cross-sections of an optocoupler; and

[0004]FIG. 3 illustrates a grid for shielding a photodiode.

[0005]FIG. 4 illustrates a shield fashioned from parallel lines.

[0006]FIG. 5 illustrates a shield fashioned from concentric circles

[0007]FIG. 6 illustrates a shield fashioned from a spiral line.

SUMMARY

[0008] In one aspect, the invention is directed to a shieldedsemiconductor device. The device has semiconductor structure with asurface and a photodiode, and a shield with one or more electricallyconductive elements and one or more apertures therethrough. The shieldis deposited over a portion of the surface of the semiconductorstructure to prevent electricla fields from reaching the photodiode andpermit light to pass through the apertures to the photodiode.

[0009] Implementations of the invention may include one or more of thefollowing features. The electrically conductive elements may define agrid, a series of parallel lines, concentric circles, or a spiral, andmay be fabricated from a conductor such as aluminum, copper, gold,silver, polysilicon, or a silicide. The electrically-conductive elementsmay be fabricted from an interconnect layer. The electrically conductiveelements may be connected to ground potential or another potential.

DETAILED DESCRIPTION

[0010] A cross-section of an optocoupler is shown in FIG. 1. There, alight-emitting diode (LED) 10 generates light that impinges on thesurface of a photodiode 20. If a transient electrical signal, such as aspike, appears at the input to the coupler, care must be taken to avoidtransmission from the LED 10 to the photodiode 20. When a large impulsesignal appears at the input to the optocoupler, an electric field may begenerated at the LED 10. If the signal is large enough, the field willcross over to the photodiode 20, inducing a current in the photodiode20. Such false indications can be avoided by placing a shield 30 toterminate the electric field between the LED 10 and the photodiode 20,as shown in FIG. 2. The electrical shield 30 allows some portion of thelight output of the LED 10 to pass through, but terminates theelectrical field.

[0011] The shield 30 can be fashioned as a grid of intersecting linesdefining square, rectangular, triangular, or openings of other shapes. Agrid 40 of square openings is shown in FIG. 3.

[0012] The shield 30 (or grid 40) could be deposited directly on thephotodiode 20 as a layer having a thickness of 100 Å to 20,000 Å,depending on the process employed to fabricate the underlying devices.Alternatively, where the process provides a metallic interconnect layer,a portion of that layer can be utilized, isolating a section of thelayer to create the shield 30 or grid 40.

[0013] The lines used to create the shield 30 or grid 40 could be aswide (or narrow) as the photolithographic process allows, e.g., 0.2 μm,up to any desired width, and the spacing between the lines could be thesame as the line width or greater to achieve a blockage of almost 90% orless. As an upper limit, one might select a spacing-to-line-width ratioof twenty-to-one, although other ratios, greater or lesser, could bechosen to suit the application. Grids having lines 1 μm in thickness andspaced at 10 μm, providing a blockage of approximately 10%, have beencreated successfully. Where a preexisting interconnect layer isemployed, the design rules for the grid will be predefined by theprocess.

[0014] Instead of a grid of intersecting lines, the shield 30 could befashioned by depositing a series of parallel lines 50 as shown in FIG.5, concentric circles 60 as shown in FIG. 5, or a spiral 70 as shown inFIG. 6, again blocking the electrical field but allowing light to pass.

[0015] The lines could be fabricated from any electrically-conductivematerial, such as aluminum, copper, gold, silver, polysilicon, andsilicides.

[0016] The shield 30 or grid 40 would be connected to a point at groundpotential or another potential to help discharge any induced field. Asshown in FIG. 3, a border 42 at the periphery of the grid 40 provides aconvenient connection point.

[0017] The shield 30 may be employed in devices other than optocouplers,i.e., in any device where an electrical field requires termination.

What is claimed is:
 1. A method for fabricating an optocoupler, themethod comprising: disposing a shield on a photodiode, wherein theshield is configured to prevent electrical fields from reaching thephotodiode, and wherein the shield includes one or more aperturesthrough which light can pass to the photodiode; and enclosing a lightemitting diode with the photodiode and the shield inside a devicepackage such that light generated by the light emitting diode travelsthrough an inner space defined by the device package to the photodiodefor detection.
 2. The method of claim 1, further comprising: fabricatingthe photodiode in a semiconductor structure.
 3. The method of claim 2,wherein: disposing the shield on the photodiode includes depositing oneor more electrically conductive elements over a portion of a surface ofthe semiconductor structure.
 4. The method of claim 3, wherein:depositing one or more electrically conductive elements includesdepositing one or more conductive materials over a portion of thesurface of the semiconductor structure, wherein the conductive materialsinclude one or more of aluminum, copper, gold, silver, polysilicon, anda silicide.
 5. The method of claim 3, wherein: depositing one or moreelectrically conductive elements includes depositing the electricallyconductive elements as a portion of a metallic interconnect layer. 6.The method of claim 3, wherein: depositing one or more electricallyconductive elements includes depositing a conductive layer having athickness of about 100 Å to about 20,000 Å.
 7. The method of claim 3,wherein: depositing one or more electrically conductive elementsincludes depositing electrically conductive elements having a line widththat is between about 0.2 μm and about 1 μm.
 8. The method of claim 1,wherein: disposing a shield on a photodiode includes disposing a shieldincluding electrically conductive elements that define a grid, a seriesof parallel lines, concentric circles, or a spiral.
 9. The method ofclaim 1, wherein the device package includes electric leads, the methodfurther comprising: electrically connecting the photodiode or the lightemitting diode to the electric leads of the device package.
 10. A methodfor operating an optocoupler, the method comprising: converting an inputelectric signal into light using a light emitting diode enclosed insidea device package; transmitting the light inside an inner space definedby the device package from the light emitting diode through one or moreapertures in a shield to a photodiode enclosed inside the devicepackage; and converting the transmitted light into an output electricsignal using the photodiode.
 11. The method of claim 10, wherein thephotodiode is included in a semiconductor structure.
 12. The method ofclaim 11, wherein: transmitting light through one or more apertures in ashield includes transmitting light through one or more apertures in ashield that includes one or more electrically-conductive elementsdeposited over a portion of a surface of the semiconductor structure.13. The method of claim 11, wherein: transmitting light through one ormore apertures in a shield includes transmitting light through one ormore apertures in a shield that includes electrically conductiveelements in an interconnect layer of the semiconductor structure. 14.The method of claim 10, wherein: transmitting light through one or moreapertures in a shield includes transmitting light through one or moreapertures in a shield including electrically conductive elements thatdefine a grid, a series of parallel lines, concentric circles, or aspiral.
 15. The method of claim 10, further comprising: using the shieldto terminate electrical fields from the light emitting diode beforereaching the photodiode.
 16. The method of claim 15, wherein: using theshield to terminate the electrical fields includes connecting the shieldto a potential source.
 17. The method of claim 16, wherein: connectingthe shield to a potential source includes connecting the shield toground potential.
 18. The method of claim 10, further comprising:receiving the input electric signal through an electric lead of thedevice package.